Liquid weight measuring system



C. A. DE GIERS LIQUID WEIGHT MEASURING SYSTEM 5 Sheets-Sheet 1 Nov. 22, 1955 Original Filed Nov. 14, 1949 FIGZ INVENTOR.

CLARENCE A. DEGIERS BM/S. Oum/0440 ATTORNEY.

Nov. 22, 1955 c. A. DE GIERs 2,724,272

LIQUID WEIGHT MEASURING SYSTEM Original Filed Nov. 14, 1949 5 Sheets-Shea*` 2 INVENTOR. CLARENCE A. DEGIERS Hf @Msiwm ATTORNEY.

Nov. 22, 1955 c. A. DE GIERS LIQUID WEIGHT MEASURING SYSTEM 5 Sheets-Sheet 5 Original Filed Nov. 14, 1949 m we m m WD IT I .l mw lr MA SC L I E Am P C EC AM" m M v R A leo/ INDICATOR @M s, MW

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ATTORNEY c. A. DE GIERS LIQUID WEIGHT MEASURING SYSTEM Nov. 22, 1955 Original Filed Nov. 14, 1949 5 Sheets-Sheet 4 FIG.9

- POWER SUPPLY -o o- OSCILLATOR MT1-Egg -un; 256 2 M POWER n SUPPLY 248 254` OSCILLATOR o Vl V'l Vl l l Il L um) 252 FREQ 242 242 Q METE 242 242 258 Hl INVENTOR. 244 244' .245 CLARENCE A. DEGIIERS MSW@ ATTORNEY Nov. 22, 1955 c. A. DE GIERs 2,724,272

LIQUID WEIGHT MEASURING SYSTEM Original Filed Nov. 14, 1949 5 Sheets-Shee. 5

RATIO METER FREQ. 280

DIS.

278 OSCILLATOR 264 A POWER 9 9 Q Q SUPPLY 274 270 I\ V l 298 294 298 BIG -sL- /ilw i 3|4 3.8 m \3|2 308 MEAsuRING 320 1N VEN TUR- 'ND'CATOR cmculT CLARENCE A. DEG|ERs @am BY 322 @0M S. Mm

ATTORNEY.

United States Patent Oiitce 2,724,272 Patented Nov. 22, 1955- LIQUID WEIGHT MEASURING SYSTEM Original application November 14, 1949, Serial No. 127,076. Divided and this application August 2, 1952, SerialNo.302,298 l 14 Claims. (Cl. 73-304) The present invention relates to a system for indieating the weight of a liquid in a container. As such, the present invention is a division of my prior and copending application, Serial Number 127,076, iiled November 14, 1949, `and entitled Liquid Gravity and Weight Gauge now Patent No. 2,691,296 issued October l2, 1954. My prior application discloses and claims a liquid density or specific gravity responsive apparatus, comprising a plurality of floats of different bulk density, Within the range of the densities of liquit to be met with, for controllingla predetermined characteristic of an electric circuit as a function of the density of the liquid. In my prior application such a series of iioat elements have been arranged alternatively to vary the resistance, the capacitance, or the inductance of a circuit. One of these electrical characteristics, which may be generically included in the term impedance, can be arranged in accordance with the present invention in conjunction with more or less conventional liquid volume sensing means to provide an indication of the weight of the liquid in the container. In accordance with the present invention, the means by which the density responsive means and the volume responsive means have their respective indications or sensings superimposed one on the other or suitaf bly combined together is essentially electrical in charl acter, this electrical system being then arranged to actuate an electrical inductor. V ,i i

i Such apparatus is especially useful in jet type aircraft to` inform the pilot or other operating personnel of the weight of fuel present. Fuel tank gauges which involve means for temperature compensation, so as to indicate weight of fuel in the tank and hence the amount of available energy, instead of volume, are in production, and their performance is excellent as long as they are used with fuel having a density within the range for which the gauges are designed. But, while such gauges can compensate for minor variations in density, they `cannot give true indications of weight when the density of the fuel used can vary considerably. Most aircraft engines of the jet type will operate on fuels of Widely varying densities ranging from No. l fuel `oil to high test gasoline.

An important feature of the invention is the use of a plurality of floats of predetermined `average or bulk densities graduated within the range of the densities to be encountered, so that each float will sink orfloat independently of the others, depending upon the density ofthe liquid in which the floats are immersed, said oats being harnessed electrically to provide a progressive change in electrical resistance or reactance (either capacitive or inductive) as the density of the liquid varies`.` If a variable reactance is used, it, together with a fixed reactance of opposite sign, may be connected to form a series-resonant circuit, the resonant frequency of which is thus responsive to the density of the liquid. The resonant frequency may n be determined by conventional means.

An object of the present invention is to provide accurate and simple apparatusI which may be used in conjunction with apparatus for measuring the volume of a liquid to compensate for Wide variations in the density of the liquid, and hence to indicate the weight of said liquid, instead of its volume alone.

The above and other objects and advantages will appear more fully hereinafter from consideration of the following description taken in conjunction with the accompanying drawings in which:

Figure l illustrates diagrammatically an arrangement for a variable resistance type density gauge;

Fig. 2 illustrates diagrammatically another arrangement for a variable resistance type density gauge;

Figs. 3 and 4 illustrate an arrangement of a float and its electric contacts in which the electric contacts and leads `are isolated from the liquid;

Fig. 5 is a side elevation partly in section on the line S-S of Fig. 6 showing an embodiment of a iloat-controlled, magnetically operated switch -in a density compensator which may be used in apparatus for indicating the weight of liquid in a tank;

Fig. 6 is a view on line 6-6 of Fig. 5;

Fig. 7 is a side elevation of an installation of the ernbodiment of the invention shown in Figs.` 5 and 6, showing a second float assembly behind the rst;

Fig. 8 illustrates diagrammatically a. device for indicating the weight of liquid in a tank, in which a variable resistance type density gauge is used as a compensator with a variable inductance type fuel quantity indicator;

Fig. 9 illustrates diagrammatically an. arrangement for a variable inductance type density gauge;`

Fig. l() illustrates diagrammatically another arrangement for a variable inductance type density gauge;

Fig. ll illustrates diagrammatically `an arrangement for a variable capacitance type density gauge; and n Fig. l2 illustrates diagrammatically a device for indieating the weight of liquid in a tank, in which a variable inductance type density gauge is used as a compensator with a variable capacitance type fuel quantity indicator.

The principle of this invention is best understood by reference to Fig. l, which shows a variable resistance type density gauge. In Fig. l, there are a number of chambers (four are shown, but there may be any number) 20, in each of which is a oat 22 or 22 free to move within its confined limits, that is, from the bottom 24 of its j chamber 20 to stops 26 at the top of its chamber 20.

The float 22 or 22 is weighted as represented by crosshatched section 28, so that the float 22 or 22 will rise when it is lighter than the liquid (not shown) displaced by the oat 22or 22. The two floats 22 shown at the far right are lighter than the liquid displaced `and hence have risen against the stops 26. When the oat 22 rises and comes in contact with its stops 26, it closes the electric circuit between its stops 26, and shorts out a predetermined portion of an electrical resistance 30 that is connected by wires 33 to the stops 26?. The operation just described is repeated as many times as thereare chambers 2i), each oat being Weighted corresponding to a different bulk density so that the specific gravity or density of the liquid will be less than that of the last oat 22 resting on the bottom 24 of its chamber 20 and more than that of the rstfloat 22 which has risen against its stops 26. Floats 22 and 22 and stops 26 are ofelectrically conductive material. Thus the amount of the resistance 30 not shorted out corresponds to a definite specic gravity or density, the greater being the density of the liquid, the smaller being the effective value of the resistance 30. An ammeter (not shown), for example, could be connected in series with the resistor 30 and be, calibrated to read in terms of density when a potential n,

difference is applied by conventional means (not shown) across the endsof resistor 30.

Fig. 2 illustrates a more relined version of the invention as embodied in Fig. 1, the apparatus being shown at the bottom of a tank 34 containing liquid 36, the density of which is to be determined. In Fig. 2 are shown two weighted floats 38 resting on the bottom 40 of 'the tank 34 rand two weighted floats 38' which have risen due to their being lighter than kthe liquid 36 displaced.. Again there may be any number of iloats. Each of floats 38 and 38 is carried on an arm 42 pivoted labout a point 44 and having on its other end a contact 46. Each contact 46 is part of a switch indicated generally at 48, the other contact being shown at 50. When a float 38' rises, its arm 42 rotates counter-clockwise until contact 46 touches contact 50, thereby closing the switch. Each switch 48 is connected by wires 52 across a correspending resistor 54, all the resistors 54 being in series, so that when a switch "48 is closed, Vthe corresponding resistor 54 is shorted out. As in Fig. l, the operation just described is repeated as lmany times as there are oats 38 and 38', each oat 38 or 38 being weighted corresponding to va different density, so that the density of the liquid will be less Athan that of the last lloat 3S resting on the 'bottom 40 ofthe tank 34 and more than that of the iirst oat 38 which has risen to close its switch 48. Thus, again, the number of resistors 54 not shorted out corresponds to a definite specific gravity or density of the liquid 36, the greater being the density of the liquid, the smaller being the elective value of all the resistors 54. The density of the liquid can be indicated in the same way as described in connection with Fig. l.

III and 1V To adapt the invention, i. e., varying electrical resistance or reactance through the use of a plurality of floats of dilerent bulk densities, for use in connection with fuel lin yan aircrafts fuel tank, or for use in connection with other hazardous liquids, it is advisable to isolate the electrical portions, such as contacts and wires, from the liquid. Figs. 3 and 4 illustrate apparatus which accomplishes this object. We may refer to Figs. 3 and 4 together, for they -show the same apparatus in .two different positions. .A oat 60 of ferromagnetic material is surrounded bythe Yliquid (not shown), the `density of which is to be determined, land is free .to move from the bottom 62 to the top 6;4 of a chamber 65. The lioat 60 will be in theformer position when its bulkdensity yis greaterthan that of the liquid and in the latter position Vwhen'its bulk density is less than that of the liquid. As the `float 60 rises, a magnetic `coupling between the oat and a .magnet 66 .causes magnet 66 to rotate counterclkwise about a pivot point 68 on a bracket 78 until a contact 70, carried on an arm 72 attached to magnet 6.6, @touches ya Vcontact 74, thus closing a ,switch formed byfcontacts 70 and 74. Wires 76 may connect contacts 70.and 74 across a portion of a resistance or a reactance (not shQwn), thus .shorting out said .portion when the tioa 60 has risen against the top 64 of vits chamber '65, i. e., when 4the float -60 is ,of a bulk density `less vthan that o f the liquid. It is to be understood that magnet 66, arm 752, bracket 7.8, Pivot point 68, contacts 70 and 74 vand the wires 76 are housed in a sealed chamber S0, and are thus completely isolated from the liquid. With a plurality of installations as shown in Figs. 3 and 4, .but withlioats vof different bulk densities, the same elfect will be obtained as explained in connection with Figs. l and 2.

V and VI type tobe described.

lt is to be understood that the float assembly shown in Figs. 5 and 6 is but one of several float assemblies in the actual gauge, the oats being, as before, of different bulk densities graduated within the range of densities to be encountered. Fig. 7 shows one assembly mounted behind another and will be best understood after considering Figs. 5 and 6, in which a loat arm 1001Carries a spherical oat 102 on one end, and a bifurcatedl boxlike frame 104 on the other. Frame 104, which is vsupported on `pivots 106, also supports a pair of magnets 108, one being mounted on each end of frame 104. A switch housing, indicated generally at 110, 'is centrally disposed in frame 104 and is vsupported on a hollow pedestal 114 which is mounted on a sealed housing 112 which may serve as a base for all the float assemblies. The switch housing comprises a sealed hollow drum having an annular shell 116 and double end plates 118 and 124 which are soldered together. Plates 118l carry pivots 122 which support a switch rocker arm (to be described), while plates 124 carry the float arm pivots 106 in alignment with pivots 122. All pivots or bearings may be jewels, in order to reduce friction. This is desirable because of the low power available. The jewels may also serve as linsulators for the moving parts inside the switch housing 110.

Centrally mounted on the pivot pins 122, inside the switch vhousing 110, is a switch rocker arm 126, box-like in structure, of electrically conductive material and provided with a pair of iron pole pieces 128, one on each end of the switch rocker arm 126. In vertical cross-section, the iron pole pieces 128 resemble circular arcs, the centers of which are yon the axis of the ytioat arm pivots 106 and the pivot pins 122. The switch rocker arm 126 is provided with a pair of silver spacers or contacts 129 equidistant from the axis of the float arm pivots 106 and the pivot pins 122.

When the float 102 rises, due to its bulk density being less than that of the liquid surrounding it, the lloat arm rotates counter-clockwise as seen in Fig. 5. Magnetic coupling between the magnets 108 and the iron pole pieces .128 causes switch rocker arm 126 likewise to rotate counter-clockwise. Thus the switch rocker arm 126 follows the movement of the iioat arm 100 as -the float 102 rises or falls. As a result, when the float 102 rises, vthe pair of silver spacers `129 make contact (Fig. 5) one with each of a pair of brushes 130 anchored by rivets 132 on insulating material 134 on the kbottom of the switch housing 110. Also anchored by the rivets 132 are the ends of lead wires 136, shown partially dotted, which are connected across part of the electric resistance or rea'ctance (not shown), the value of which is to be responsive to the specific gravity or density of the'liquid. The resistance or reactance may be located in the housing 112. The electrical connections in the case of Figs. 5 and 6 may be exactly the same as in the embodiments of the invention previously described in connection'with Figs. 1, 2, 3 and 4 or as in the embodiments of variable reactance types of specific gravity gauges to be described.

VII

Fig. 7 shows how ka second lloat assembly 142, a's described in connection with Figs. 5 and 6, may be mounted behind a `lrst oat assembly on the base-144. As many such assemblies may thus be mounted as 'desired or needed.

VIII

One of the important uses which can be made of the invention is as a density compensatorin a gauge for indicating the weight .of .a liquid, suchas gasoline, in a tank. To make such a gauge, the vdensity compensator ,may be inserted in a circuit which would otherwise constitute a gauge for indicating merely the volume of liquid. Fig. 8 shows diagrammatically a circuit including'a density compensator of the variable resistance typewhich can be used to indicate the weight of the liquid. The comn `illustrated in Fig. 2, although it could just as well be any one of the variations. `The compensator 150 controls, in the manner described, the effective value of a group of resistors 152, 154, 156 and,15,8, only `fourbeing shown.

, The fuel volume measuring element, indicated generally at 160, is a variable inductance coil 162which is responsive to the liquid level by means of a oat 164 connected `to a permeable core 166 arranged to move into or out of the coil 162 as the` oat 164 rises or falls in response to changes in liquid level, the liquid not being shown. This movement changes the inductance of the coil 162. It is to be noted that the liquid level responsive device, here the coil 162, in itself compensates for minor changes in liquid density, but is ineffective when the density varies widely, as `it may from time to time in the` case of fuel in the tanks of jet type aircraft. The coil 162 is an element of a bridge circuit which includes, in addition to coil 162, a reference `coil 168, and the secondary 172 of a transformer 170 which may be energized by an audio frequency power supply 176 connected across the primary 174 of the transformer 170. The output of the bridge circuit is taken between a tap 178 on the secondary 172 and a point 180 between the coil 162 and the reference coil 168, and is fed to an output transformer 182. The secondary 184 of the transformer 1`82`is shunted by the resistors 152, 154, 156 and S, and by another resistor 186 of the density compensator 150. While shunt connections of the resistors have been shown, series connections or potentiometer connections rnay be used. A measuring circuit 188 is connected across the secondary 184 of the output transformer 182 and will detect the output of the bridge circuit, and may compare it with a reference signal from an indicator 190 by a feed-back connection 192. The resulting signal may be amplified by an amplifier 194 and be made to control the indicator 190. This, in effect, is a servo type circuit,

In operation, the bridge will be arranged to be in balance (that is, no output) when there is no liquid in the tank. Under this condition, all the floats` of the compensator will be down, a condition which would correspond to having the tank full of very light liquid. However, since the output is zero, there will `be no error in the reading of the indicator 186. As the tank is lled, the bridge will become more and more unbalanced due to change in the inductance of the coil 162, and the output" of the bridge to the measuring circuit 18S will become pro gressively greater. If the density of the liquid now changes, the compensator 150 will further modify the output of the bridge by cutting out resistors or by adding them to the circuit depending on the direction of the variation. Thus, the inal reading of the indicator will be a truer indication of the contents of the tank by weight than if the compensator 150 were omitted. lt should be understood that the volume-responsive element 160 could just as well be capacitive, in which case the reference coil 168 would be replaced by a reference capacitance.`

The invention, as embodied in a` variable reactance type specific gravity or density gauge, may be understood by referring to Fig. 9, in which any number `of oat assemblies collectively indicated at 210 (only four are shown) are near the bottom of a tank 212 containing liquid214, the specific gravity or density of which is to be determined. Each float assembly comprises a oat 216 or 2,16 carried on one end of an arm 218 pivoted at a point 220. Each float 216 is shown at the lower end of its arc, while each float 216' is shown at the upper end of its arc. On the other end of each arm 218 is an electric contact 222, which is part of a switch indicated generally at 224,the other contact being shown at 226. When a float 216 travels upwardly along its arc, due to its bulk density being less than that of liquid 214, its arm 218 rotates counterclockwise (as `seen in Fig. 9)` until contact 222 touches contact 226, thereby closing switch 224. vEach switchl 224 is connected across a respectively predetermined portion 225 of an inductance 228, so that when a switch 224 is closed, its corresponding predetermined portion 225 of inductance 228 is shorted out. Coil 228 is shown as a single coil tapped at various sections, but it Will be understood that a number of separate coils may be used.` The operation just described may be repeated as many times as there are floats 216 and 216', each float 216 or 216 being weighted corresponding to a different bulk density, `so that the specific gravity or density of the liquid 214 will be less that that of the last float 216 at the lower end of its arc and greater than that of the rst float 216 at the upper end of its arc. Thus, the amount of the inductance 22S not shorted out corresponds to a definite specific gravity or density of the liquid 214, the greater being the specific gravity or density of the liquid, the smaller being the effective value of the inductance 228. Coil 228 is connected in series with a condenser 230, which together form a series-resonant circuit, the resonant frequency of which is a definite function of the value of the inductance 228, and is given by the formula cillation of oscillator 232 may be measured by any convenient form of frequency meter, shown in block form at 236, which may be calibrated to indicate specific gravity or density directly.

`In operation, the density-sensitive floats 216 and 216 may be placed in tank 212 for the purpose of determining the specific gravity or density of the liquid 214 therein. If it be assumed that the liquid 214 is of an average density, the system can be adjusted so that, for example, half the iloats 216 are at the bottoms of their arcs and the other half are at the tops of their arcs. This means that half the switches 224 will be open and the other half will be closed. Thus some of the turns of coil 228 will `be shorted out, causing the oscillator 232 to generate a signal of a denite xed frequency. If a lighter liquid is now placed in thetank 212, the oat 216' having the greatest bulk density will also sink, thereby opening its switch and increasing the inductance of the coil 228, thus causing the oscillator 232 to generate a signal of lower frequency. However, if the substituted liquid has a greater density than does the original liquid 214, the oat 216 having the smallest bulk density will rise, thereby closing its switch 224. This shorts out more of the coil 228 and decreases its inductance, thereby causing the oscillator 232 to generate a signal of greater frequency. The frequency meter 236 canV then be conveniently calibrated to indicate specific gravity density directly.

250, lthe specific gravity or density of which is to be deter-y mined.` The floats 244 and 244 have bulk densities graduv ated within therange of densities to be encountered, asv

exalnedfin the `descriptien ofFis. 9- Each'ileat '244 Qr 244'is adjusted so that, Yresponsive to -the densi-ty of liquid 250, it will approach or recede from its respective coil 'As a iloa-t 244 rises inthe liquid 250 surrounding it, it approaches its corresponding coil v240, increasing the induetance thereof, the 'floats 244 and 244 'being of ferromagnetic material. As before, the rest ofthe `circuit comprises a Acondenser 252 in `series with coils 240, an `oscillator -254 connected -a'lso to a power supply 256 and a -frequency meter 258 `which may be conveniently calibrated toiread specific gravity or density directly.

'For operation, again the system `can b e adjusted so 'that for liquid of average `specific gravity or density, 4halftl'ie floats, i. e. floats 244 will be down (of bulk density greater 4than that of the liquid) vandl lhalf the floats, i. e. floats 244' will be up (of bulk ydensity less than that of the liquid), result-ing in a mid-scale'reading of the frequency meter 258. If liquid of ygreater than average specificgravity or 'density is substituted, one of the floats 244 rwill rise, thus coming closer lto its corresponding rcoil 240 and increasing its inductance. This ldecreases the frequency generated by the oscillator 254 again in accordance with the formula rThe .circuit shown in Fig. 1l is in general similar to those of Figs. 9 and 10, in that .it contains a series-resonant circuit including inductive and capacitive elements, However, in this case, instead of varying the inductive element .responsive to changes in the specific gravity or density ,of the liquid under test, fas done in the circuits of Figs. 9 and l0'the -capacityis changed. The arrangement .of the `floats shown in Fig. ll at `2.60 and 260 and their corresponding switches, `shown generally in Fig, .ll `at 2,62, Vifsexactly the same .as .in the `apparatus shown in Fig. 9 and need not be .described again. .Again the float vassembly is villustrated near the bottom 264 of a tank 26,6.containing the liquid 268 under test. The series.- resonant .circuit in the case of Fig. 11 starts with a lead wire 277i) from a variable frequency oscillator 272, .and .comprises a fixed inductance 274 in lseries with 'a .condenser ,276, which Ais connectedby a lead271 back into .the oscillator 272. The ,oscillator'272 `again yis energized by a .power supply 278, but as a variation from the circuits described in `connection with Figs. 9

and .10, theoscillatcrzn is arranged to feed into a frequency `,discriminator y.280 from which suitable currents may .be derived to voperate va .ratiOIIllfI 282 .and ia Pointer (not shown). Y

Qne side of Aeach Yswitch .,262 r is Vconnected to the `lead 27:1 .and va condenser `284 is connected in series with the other side of each switch 262 respectively. The .side of each condenser 284 remote from its corresponding switch 262 is connected to the end of the coil 274 remote from the oscillator y272. Thus when afloat 260 is at the top of its arc, due to its bulk density being less than that of the liquid 268, vits corresponding switch 262 is closed. With the switch in this condition, the corresponding lcondenser 284'will be `connected .in parallel with .the condenser 2,7'6.

in operation, the ,apparatusu may be adjusted so that for a-liiuid ef aver-ase sreicgrevty Gf density, half the. floats, i. fe. the Boats "2,60 will ybe 'at ,the 'bottom of `their arcs-and h alf the floats, i,` e. the `floatsy 260' will be lat the tops-oftheir arcs. If a liquid of greater than average specific gravity or density lis substituted, one ofthe oats 260fwi1l rise, thus closing'its switch y2'62, and con v-necting itscorresponding condenser 284 in parallel with the condenser 276. Thereby, the overall capacity vof the vseries-res'ona-nt circuit including the coil '274 yand the condenser 276 is increased, :since when two condensers are connected in parallel, the equivalent series capacitance is the sum of the capacitances of the two lcondensers. Conversely, if a liquid of less than average specific gravity or density is substituted, one of the floats 260 will sink, thus opening its switch 262 and decreasing the capacitance of the series-resonant circuit by the value yof its corresponding condenser. As is the case in the circuits shown in Figs. 9 and 10, these changes 'in the 'specific gravity or density of the liquid under test are reflected in changes in the frequency of the signal `generated by the oscillator 272. When the capacitance increases (due to an increase in specific gravity or density), the generated frequency decreases, and vice versa. These frequency changes are in turn reflected by changes in the indicator readings, as in the othercircuits.

XII

As is the case with a variable resistance type gauge, one of the important uses which can ybe made of a variable reactance type specific gravity or density gauge is as a density compensator in a gauge for indicating the weight of a liquid, lsuch as gasoline, in .a tank. To make such a gauge, the density compensator may be inserted in a circuit which would otherwise constitute agauge for indicating merely the volume ofliquid present. Fig. l2 shows diagrammatically a circuit including a density compensator which can be used to,in dicate the weight of a liquid 290 in a tank 292. In Fig. l2, the compensator, shown near the bottom 294 of the tank 292, is indicated generally at 296, and is similar to that illustrated in Fig. 10, except that as a matter of convenience, the unit is turned upside down. The compensator 296, which, in the manner described, controls the inductance of a ygroup of coils 29S, couldv just as well be of the variable capacitance type, as shown in Fig. l1.

The fuel volume responsive element is a condenser, formed of inner and outer spaced concentrically-positioned metal cylinders 302 and 304, which are supported vertically in the tank 292 by insulating supports,` as at 306, which may be formed of any suitable linsulating material. YThe cylinders 302 and 304 extend substantially from the bottom to the top of the tank 292, so that the capacitance of the condenser 300 is a function `of the depth of liquid in the tank 292. The depth 0f liquid between the plates 302 and 304 of the condenser 300 is the same as that in the rest of the tank 292. The capacitance is a function of liquid level because capacitance depends upon the dielectric constant of the insulating medium between the plates of the condenser, gasoline, for example, having a dielectric constant of approximately two, the dielectric constant of air beingU one. Therefore, when the air between the condenser plates 302 and 304 is replaced by gasoline, the capacity of the condenser increases by a factor of two, with proportional changes taking place when the gasoline only partially fills the space between the condenser plates 302 and 304.

A fuel quantity indicator of the variable capacitance type in itself compensates for minor variations in liquid density, but is ineffective when the density varies over a wide range, as it may in the case of fuel for most jettype aircraft engines. In such a case, the density compensator will substantially reduce the eiects of such wide variations.

ln the apparatus shown in Fig. l2, the circuit may be energized by an audio frequency power supply 3.08. The output of the power supply 308 is applied to abridge circuit comprising an input transformer 310, the volume responsive condenser 300, and a reference condenser 312, both of the last-mentioned elements being in series with the output of the transformer 310. The output of the i ple, in pounds of liquid.

bridge circuit is, taken from a point 314 on` lthe secondary of the transformer 310 to a second point 316 `whichis grounded between the conden-sers 300 and 312. Between points` 314 and 316 are the density compensator 296 and `the primary of an output transformer 318 in series. The output secondary of `the transformer 318 feeds into a measuring circuit 320 which will detect theoutpuvt of the bridge circuit and in turn will operate an indicator .322 which may be conveniently calibrated to read, for eXam- For operation, the bridge circuit may be adjusted `so that when there istno liquid in the tank, the bridge circuit will be in balance (that is, no output). Under` this condition, all the oats of the compensator` 296 will be down, a condition corresponding to having thetank 292 filled with liquid of very low` specific gravity. However,

`since the output is zero, there will be no error in the reading of the indicator 322, As the tank 292 is `filled, the bridge will become more and more unbalanced, due to the increase (already explained) in the capacitance ofthe condenser` 300. The result will be a greater and greater output tothe measuring circuit 320. If the density of the liquid now changes, the inductance of the coils 298 in the compensator2v96 will also change, thus modifying the output tothe measuring circuit 320 through the transformer 318 by causing a smaller orrgreater voltage to be applied thereto, dependingupon whether the liquid density `has increased or decreased. If the density basincreased, more floats of the compensator 296 willrise, thus decreasing the inductance of the coils 298. 1 In this event, a greater voltage will be `applied across the transformer 31S, thereby increasing the output to the measuring circuit 320.

The described apparatus will` be seen to `provide a simple, accurate and reliable measurement and indication of the specic gravity or density of a liquid in accordance with the objectives of the present invention, but it is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other wayswithout departure from its spirit as defined by the following claims.

What is claimed is:

l. A system for indicating the weight of a liquid in a container, comprising an electrical network providingtwo electrically spaced circuit output terminal points, at least two circuit branches connected between said points, an

e electrical impedance means having an'impedance value which is a function of the volume of said liquid in said container connected in one of said circuit branches, a compensating electrical impedance means connected in another of said circuit branches, means for energizing said network by applying to said circuit branches including both said impedance means respectively A. Cf electrical energy of opposing phase, output circuit means connected to said terminal points; means responsive to the density of the liquid in said container, an electric circuit branch which is electrically coupled to said output circuit means, means for controlling the impedance of said electric circuit branch by said density responsive means and in accordance with the density of said liquid, and an electrical indicating means electrically coupled to said output circuit means and responsive to current ow therein as affected by the impedance of said electric circuit branch for indicating the weight of the liquid in the container.

2. A system for indicating the weight of a liquid in a H container, comprising an A.C. energized bridge circuit, means responsive to the volume of the liquid in said container for varying the reactance of one arm of said bridge circuit, a plurality of electric circuit components, means` responsive to the density of the liquid in said container and constructed and arranged to control the effective impedance of said electric circuit components, means connecting said electric circuit components into `the output of said bridge circuit, so as to introduce into the electrical output of said bridge circuit an electrical function ofthe .density of said liquid, and means responsive to theioutput of, `said bridge circuit `as `affected by the density of said liquid as aforesaid for indicating a value proportional to the weight of the liquid in said container. e

`3. A system in accordance with claim 2, wherein said volume responsive means comprises a capacitorincluding electrodes which arelocated in said container so as `to be immersed in the liquid therein to an extent dependent upon the level of such liquid, so that the capacitance `of said capacitor is a function of liquid level, said capacitor being connected in one arm of said bridge circuit.

4.` A systemin accordance with claim 2, and wherein said volume responsive `means comprises a variable inductor, the inductance of which is controlled as a predetermined function of the` level of the liquid in said container, said variable inductor being connected in one arm of said bridge circuit. u

S. A system for indicating the weight of a liquid in a container, comprising means responsive to the volume of the liquid in the container, an electrical bridge circuit connected to be energized from a` source of electric energy and including one arm, the impedance of which is controlled by said volume responsive means as a function of the volume ofthe liquid in the container, means responsive to the density of the liquid in the container, electrical means controlled by said density responsive means and electrically connected with the output of said bridge circuit for electrically introducing a function of the density `of said liquid into the electrical characteristics of the output ofthe bridge circuit to produce a resultant electrical output, and` electrically controlled indicating means responsive to said resultant electrical output of said bridge circuit as affected both by said volume responsive means and by said density responsive means for indicating the Weight of said liquid. u `6. Asystem for indicating the weight. of a liquid in a container, comprising means responsive to the volume of the `liquid in the container, an electrical bridge circuit connected to` be energized from an A. C. source of electric energy and including one arm, the impedance of which is controlled by said volume responsive means as a function of the volume of the liquid in the container, a transformer having its primary winding connected to the output of said bridge circuit, `electrically controlled i'ndicating` means connected to the secondary winding of said transformer, means responsive to the density of the liquid in the container, and electrical means controlled by said density responsive means and electrically connected to one of the windings of said transformer for introducing a function of liquid density into the electrical control of said indicating means, so that said indicating means may directly indicate the weight of the liquid in said container.

7. A system according to claim 6, wherein said electrical means controlled by said density responsive means is effective to control the impedance of an electrical branch connected in parallel with the secondary winding of said transformer.

8. A system according to claim 6, wherein said electrical means controlled by said density responsive means is effective to control the resistance of an electrical branch connected in parallel with the secondary winding of said transformer.

9. A system according to claim 6, wherein said electrical means controlled by said density responsive means is eiective to control an electrical impedance which in turn directly affects the currentflow through the primary winding of said transformer.

l0. A system according to claim 6, wherein said electrical means controlled by said density responsive means comprises a variable inductance connected in series with the primary winding of said transformer across the output of said bridge circuit.

l1. A system for indicating the weight of a liquid in a container, comprising a bridge circuit, said bridge circuit including tirst 'variable reaetance smeans responsive to :the `volume `of said liquid,l second rcactance means :ofthe came lsign as said first reactance-means, and 'third re'- actance means 'comprising the input of ysaid bridge, power supply to energize said input, the output 'of said bridge being connected lfrom a point on said third re-' lactance means to a point between said first and second reaetance means, a variable resistance type density lcompensator Aresponsive to lthe density of the "liquid inthe container -for controlling the resistance vof an electrical branch in yaccordance with the 4density `of ythe liquid in the container, means electrically connecting said 'electrical branch into vthe output of said bridge', and indicating means Aresponsive Ato the output of said bridge as affected by lsaid compensator as aforesaid for indicating' the weight of lsaid liquid inthe container.

12. A system for indicating the weight of a liquid in a container, comprising a 'power supply connected across the primary v`of an input-transformer, a 'variable inductance responsive to changes in the'volume of said liquid,

a reference inductance, an electric circuit connecting'said variable inductancel and said reference inductauce in series across thesecondary of rsaid finput transformer, said variable inductance, said reference inductance, yand said secondary of said input transformer forming a bridge circuit, vthe output of said 'bridge circuit thus being responsive to the volume of ysaid liquid, an output transformer having its primary winding connected from a point on the secondary of said input transformer to a point between said variable inductance `and said reference inductance, a measuring circuit shunted across the -secondary winding of said output transformer and responsive to the output ofisaid output transformer, a variable resistance type density compensator responsive to the density of the liquid in the container and also vshunted across the secondary winding of said output transformer, ythe input to said measuring circuit thus being further responsive tothe density of said liquid, said measuring 4cirj cuit including-an indicator for indicating 'the weight of said liquid.

13. A system for indicating the weight of a liquid in a container, comprising a bridge circuit, said bridge circuit including first variable reactance means responsive 'to -the volume of said liquid, second reactance means ofthe same sign as lsaid tirst reactance means, and a third reactance meanswhich is the inputof said bridge, avariable 'reactance density compensating device responsive to the density Yof `the liquid in the container and connected in series with the output of `said bridge, said output and said compensating device being connected from a point on said third reactance means to a point between said irst and said second reactance means, and indicating apparatus responsive to the output of said bridge as affected by said compensating device for measuring the weight of said liquid.

14. A rsystem for indicating the weight of aliquid in a'container, comprising a power supplyA connected across the primary of yan input transformer, a variable capaci- 'tance responsive to changes in the volume of said liquid, a lreference capacitance, an electric circuit connecting said lvariable capacitance and said reference capacitance in series across the secondary of said input transformer, said variable capacitance, said reference capacitance, and said `secondary of said input transformer forming a bridge c'ircuit, the output of said bridge circuit being responsive'to the volume of said liquid, an output transformer, a variable inductance density compensating device responsive to the density of the liquid in the container and connected in `series with'the primary Winding of said output `transformer, said compensating device and said primary wind ing of said output transformer being connected by an electric circuit'from a point on said secondary of said in`- put transformer to a grounded point between said variable capacitance landsaid reference capacitance, and a measuring circuit including an indicator responsiveto the output of said output transformer for measuring the weightof said liquid.

References Cited lin the file of this patent UNITED STATES PATENTS 

